1. Quench Protection Measurements & Analysis
G. Ambrosio
MQXF International Review – CERN, June 7th – 10th, 2016

2. Quench Protection Strategy
Outline
Quench Protection Strategy
Main elements
Open questions
Inner layer heaters
CLIQ
MQXFS1 Test Results
Heater delays
Dynamic effects
Updated Simulations
Conclusions
G. Ambrosio - MQXF International Review

3. MQXFA/B Main Parameters
Unit
MQXFA/B
Coil aperture mm
150
Magnetic length m
4.2/7.15
N. of layers 2
N. of turns Inner-Outer layer
22-28
Operation temperature K
1.9
Nominal gradient
T/m
132.6
Nominal current kA
16.5
Peak field at nom. current T
11.4
Stored energy at nom. curr.
MJ/m
1.2
Diff. inductance
mH/m
8.2
Strand diameter
0.85
Strand number 40
Cable width
18.15
Cable mid thickness
1.525
Keystone angle
0.4
MQXF Magnets & Protection

4. Quench Protection Plan
Elements:
No Energy Extract.
Heaters
CLIQ units
VT for detection
Strategy:
Outer Layer heaters  protection & some redundancy
IL heaters & CLIQ  reduced hot spot Temp. & additional redundancy
Heaters can be optimized for low current (because there is no dump)
MQXF Magnets & Protection

5. Instrumentation for Quench Detection: 4 voltage taps per coil
2 VT per lead around Nb3Sn-NbTi splice
Detection:
Threshold: 100 mV
at high current
Verification: 10 ms
Power supply switch:
delay: 5 ms
MQXF Magnets & Protection
Paolo Ferracin

6. Protection Heaters
Quench heaters have been designed using copper plating for inner and outer layer:
Two strips on each side of the outer layer
“High Field” and “Low Field”
One strip on each side on the inner layer
Inner layer 40% polyimide free
Outer Layer
Inner Layer
MQXF Magnets & Protection

7. Proposed QH Connection Scheme
Each QH supply is connected to 2 strips in series
Connection scheme that compensates the voltages induced by CLIQ and QH
Connecting in series 2 strips attached to different poles reduces the effects of failures (hot-spot temperature, voltage distribution)
LF3
LF2
HF3
HF2
HF4
HF1
IN3
IN2
LF4
IN1
IN4
LF1
Standard LHC quench heater power supply
Charging voltage: 900 V
Voltage to ground: ±450 V
Capacitance: 7.05 mF
Note: 2x 450 V, 14.1 mF modules in series
LF1
IN1
IN4
LF4
IN2
IN3
HF1
HF4
Only a quarter of the circuits shown
HF2
HF3
LF2
LF3
E. Ravaioli, and G. Sabbi

8. OL & IL Protection Heaters
Outer Layer heaters: very reliable
Survived large number of quenches and heater studies on many LARP magnets
Inner Layer heaters are not pushed toward the coils as Outer Layer heaters  risk of “bubbles”
Polyimide perforation (40%) should help
Different designs
CERN design (E. Todesco)
LARP design (T. Salmi)
MQXF Magnets & Protection

9. MQXFS1 Bore View (after test)
Several bubbles on two coils
Very few bubbles on two coils
Different heater design
Different fabrication site
Heater tests Y/N

10. Coupling-Loss Induced Quench system
CLIQ
Coupling-Loss Induced Quench system
Successfully tested on Nb3Sn short models and NbTi long magnets
Presentation showing concept and validation (by E. Ravaioli) available upon request
Note: the failure of a CLIQ unit can be simulated by single magnet analysis because of the diodes
MQXF Magnets & Protection

11. Simulated Currents in the Circuit
Q2a/Q2b
Q1/Q3
CLIQ units for Q2a/Q2b
Charging voltage: 1000 V
Capacitance: 40 mF
CLIQ units for Q1/Q3
Charging voltage: 600 V
Diodes
Hot-spot temperature Thot~230 K
Currents through the SC Link (no fault case)
Main leads: Magnet current ± AC oscillations, 1.5 kA, 12 Hz
Trim leads: Their initial current + AC pulse, 500 A, 12 Hz
CLIQ
Simulations performed with TALES

12. Work in progress to address open questions:
CLIQ
Work in progress to address open questions:
“Investigate further the CLIQ technology, in particular, assess the long-time reliability and availability when applied for Nb3Sn coils, …”
Recommendation from Circuit Review
Impact on other elements of the circuit, for instance the superconducting link.
Large number of failure cases have been studied and addressed
Diodes are used to mitigate some failure scenarios
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13. Test Results
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14. MQXFS1 Heater Effectiveness
Heaters tested in “MQXFC-like” conditions
 MQXF heaters can quench magnet at I < 2 kA
Starting configuration “2 strips in series” is OK
IL strips can be powered singularly if needed
G. Chlachidze, S. Izquierdo-Bermudez & E. Ravaioli
1 IL strip per HFU
2 OL strips in series
2 IL strips in series

15. MQXFS1 Heater Delay Tests - I
OL heaters: very good agreement with simulations
12 ms
18 ms
Simulations performed with CoHDA by T. Salmi (TUT)

16. MQXFS1 Heater Delay Tests - II
IL heaters: longer delays than in simulations
18 cpr 10 ms
Simulations performed with CoHDA by T. Salmi (TUT)

17. Very good match btw computed and measured dynamic effects
Ldiff ~ 50% Lnom
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18. Updated Simulations
G. Ambrosio - MQXF International Review

19. Peak Temperatures and Voltages
Scenarios: 1 2 3 4 5 6
OL heaters Y F1 F2
IL heaters N
CLIQ
Hot-spot Temp. K
219
229
228
324
349
363
Coil-Ground V
507
314
287
467
579
Turn-Turn 31 32 35 54 65 71
Layer-Layer
497
259
426
572
670
Mid-plane
509 34 33
237
376
Assumptions:
Detection mV
100
Verification ms 10
Heater switch delay 5
Circuit
Single Power Converter for Inner Triplet
Energy extraction NO
Dynamic effect on inductance
YES
Quench back
Quench propagation OL-IL
YES, simulated
Simulations performed with Tales by E. Ravaioli
Failure scenarios: F1
one OL-HF circuit ( = 2 strips) F2
one OL-HF circuit and one OL-LF circuit, on the same coil and same side (= 4 strips)
Note: Energy extraction reduces hot-spot temperature by ~10 K, and increases coil-ground voltages by ~400 V in some cases
G. Ambrosio - MQXF International Review

20. Code Benchmarking & Comparisons
Several codes are being used
For quench simulations: Tales, QLASA, ROXIE, ...
For Quench Heater delays: CoHDA
All codes have been tested using Nb3Sn magnet data
Direct comparisons:
Code: A B
OL heaters Y
IL heaters N
CLIQ
Hot-spot Temp. K
324
320
Coil-Ground V
287
357
Turn-Turn 54 56
Layer-Layer
426
560
Mid-plane 33
Code A
Tales
Analysis by E. Ravaioli
Code B
QLASA & ROXIE
Analysis by V. Marinozzi
G. Ambrosio - MQXF International Review

21. IL and/or CLIQ reduces Hot Spot by 100 K
Conclusions
Tests and simulations are demonstrating that MQXF magnets can be protected using Outer Layer heaters
Very reliable solution based on years of LARP tests
IL and/or CLIQ reduces Hot Spot by 100 K
Additional redundancy can be provided by Inner Layer heaters and/or CLIQ
Plan will be finalized after Prototype tests
Technical review
G. Ambrosio - MQXF International Review

22. BACKUP SLIDES
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23. 6. Experience on MB heaters failure
According to MB_quench_heater_failures.ppt (M. Bajko) and EDMS :
12 magnets were refused after delivery to CERN due to quench heater failure
11 magnets were reworked before delivery to CERN due to quench heater failure
Around 2/3 of the failures are on the magnet extremities
According to
In total, 10 magnets showed quench heater issues:
5/10 magnets were replaced during LS1 (all produced by the same company).
In 2 magnets, the wire connection was repaired during LS1.
In 3 magnets, the HF heater was replaced by the LF.
In total, 32 heater power supplies failures were identified (mainly due to a switch related issue):
All replaced
It never happened in a quenching magnet (heater power supply voltage is always monitored in the LHC)
It never happened to have two heater power supplies failing in the same magnet.

24. 6. DS-11T vs MB If 1 QH power supply fails:
Circuit 3
Circuit 2
Circuit 1
Circuit 4
11 T MB
If 1 QH power supply fails:
Heater power supply will be replaced during the next access.
If 2 QH power supply fail:
Beam dump and heater supply replacement.
If one heater circuit fail (1/4):
Next access heater re-wired to the low field heater.
During next long shut down the magnet might be replaced.
If more than two circuits fail: individual case needs to be studied.
If 1 QH power supply fails:
Heater power supply will be replaced during the next access.
If 2 QH power supply fail:
Beam dump and heater supply replacement.
If one heater circuit fail (1/16):
During next long shut down the magnet will be replaced.
If more than two circuits fail: individual case needs to be studied.

25. Case 4 Coil-Ground
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26. Case 4: Coil-Ground
G. Ambrosio - MQXF International Review

27. MQXFS1 Heater Tests - II Outer Layer heater delays =< computed
Inner Layer heater delays > computed
Worse at mid & low I
103:
CERN-style heaters tested in MQXF-like configuration
MQXFSM1:
LARP-style heaters tested with lower power density than nominal

28. Heaters have been designed & optimized by
Heaters Optimization
Heaters have been designed & optimized by
M. Marchevsky (LBNL) design w/o copper plating
E. Todesco (CERN) design with copper plating
T. Salmi (Tampere Univ.) delay computation & optimizat.
2D thermal simulation using CoHDA
Verification & calibration using LARP HQ magnets
Criteria adjusted from Tmax = Tcs  Tave = Tcs
HQ02a-b outer layer
MQXF Magnets & Protection

29. Protection at Low Current
Without energy extraction MQXF magnets may need active protection also at low current (1 kA)
Quench initiation in a few points per coil is enough
Heater design can be adjusted to do it in case present heaters cannot (tests in progress)
 Super-Heating stations
MQXF Magnets & Protection